1. Field of the Invention
This invention relates to rotational coupling devices such as brakes and clutches and, in particular, to a rotational coupling device that improves retention of a drive key during shipping, installation, and operation of the device.
2. Discussion of Related Art
Rotational coupling devices such as clutches and brakes are used to control transfer of torque between rotational bodies. One type of conventional device is illustrated in U.S. Pat. Nos. 5,119,918, 5,285,882 and 5,971,121, the entire disclosures of which are incorporated herein by reference. This device includes a rotor that is coupled to an input shaft for rotation with the input shaft about a rotational axis. A field shell is also disposed about the input shaft on one side of the rotor and is fixed against rotation. The field shell defines radially spaced, axially extending inner and outer poles between which an electrical conductor is disposed, facing the rotor. A brake plate is coupled to the field shell and axially spaced from the field shell. The brake plate is disposed on a side of the rotor opposite the conductor. An armature coupled to an output member is disposed on the same side of the rotor as the brake plate and is disposed axially between the rotor and the brake plate. The armature is coupled to an output member by a plurality of leaf springs. Energizing the conductor produces a magnetic circuit in the field shell, rotor and armature that draws the armature into engagement with the rotor and couples the input shaft and output member together for rotation. Upon deenergization of the conductor, the leaf springs draw the armature out of engagement with the rotor and into engagement with the brake plate to brake the armature and output member. Permanent magnets coupled to the brake plate are also used to create another magnetic circuit between the brake plate, the field shell and the armature to assist the leaf springs in braking the armature and output member.
The rotor in the above-described rotational coupling devices is generally coupled to the input shaft using a key. In some conventional devices, the key is formed as a separate component that extends into opposed keyways in the rotor and the input shaft. During assembly of the coupling device onto an input shaft, the key must be inserted into the opposed keyways of the input shaft and rotor. Positioning the key at the proper orientation to avoid damage to the keyways is difficult and consumes valuable assembly time. Further, the key has a tendency to travel relative to the rotor and/or input shaft during assembly and operation of the device leading to misalignment of components, increased downtime and maintenance costs.
The inventor herein has recognized a need for a rotational coupling device that will minimize and/or eliminate one or more of the above-identified deficiencies.